How the 747 Got Its Hump

In the evolution of the airplane, Darwinian principles have applied unevenly

Military transport airplanes all look like Grandpa: the Lockheed C-130. It has a high-mounted wing, a stumpy-legged main landing gear in pods on the lower corner of the fuselage, and an upswept tail that incorporates a ramp door. The ramp can be lowered to the ground so that vehicles can drive in, it can be extended straight out to roll cargo pallets onto or off a truck, or it can be opened in flight to drop loads out the back by parachute.

For a brief period between World War II and the Korean War, it appeared that a very different configuration would reign, with a central pod fuselage and twin booms supporting the engines and tail—see the Fairchild C-82 Packet and C-119 Flying Boxcar in the United States and the Nord Noratlas and Armstrong Whitworth Argosy “Whistling Wheelbarrow” in Europe. But that species was doomed.

The C-130 did not spring from a clean sheet of paper. It owes a lot to some little-remembered airplanes that link it to the transport gliders of World War II and, via a forgotten experiment, to the Douglas DC-3 and its military derivative, the C-47. In 1943 and 1944, the U.S. Army Air Forces wanted to replace its C-47s with four-engine Douglas C-54 transports. This entailed replacing its transport gliders, as the steel-tube-and-fabric airplanes could not survive in tow at the C-54’s 250-mph cruising speed. As an experiment, USAAF engineers at Wright Field in Ohio stripped the engines from a war-weary C-47.

Not only could the modified airplane be towed faster, but it had a low stall speed and a good glide ratio, both of which promised to make glider landings much less dangerous.

So the Army ordered two new high-speed gliders from the Chase Aircraft Company. The XCG-18 and the bigger XCG-20 shared three features: a high wing, a short, body-mounted landing gear, and a high tail. There was no ramp, but the tail was designed to stay clear of the ground when the glider landed. The XCG-18 flew in December 1947, but the USAAF had become the U.S. Air Force, and the U.S. Air Force liked supersonic fighters and jet bombers, not poky trash-hauling gliders. Chase fitted it with two engines, producing the C-122, a handful of which were built for the Air Force. Like a dinosaur with feathers, the C-122 was a link between gliders and airplanes: It still had a towing hook and could hitch a ride from another airplane to extend its range. The bigger XCG-20 acquired engines—as the C-123—before it was built.

One of Germany’s largest wartime transports was the Junkers Ju 290, adapted from the Ju 90 airliner. The Ju 90 had a tail-wheel landing gear, with a nose-high ground attitude and sloping floor that made it hard to load cargo. Junkers engineers installed a powered ramp under the tail, which raised the airplane into a horizontal attitude as it opened. After the war, the USAAF tested a captured Ju 290 (nicknamed “Alles Kaput”), and the ramp subsequently appeared on the C-123.

Fairchild, which acquired Chase, built more than 300 C-123s. The C-123 still looks enough like a C-130 to double for the Lockheed airplane when a movie script calls for a military transport and the Air Force won’t cooperate. C-123 credits include Con Air, Outbreak, and most Vietnam war movies in which the bad guys are Americans.

The fossil record of the creatures leading to the C-130 is hard to find because it includes a few obscure aircraft. Tracing the lineage can be more difficult if the missing link was never built.

In March 2001, Boeing unveiled the concept for an airplane called the Sonic Cruiser. A canard (tail-first) design with a compound-sweep wing and engines carried on a “back porch” extension of the wing, it looked different from any airplane Boeing had ever built. The missing link, hiding in a NASA presentation in an obscure corner of the Internet, was a Boeing supersonic transport design that—except for a pointy nose and different engines—was clearly the Sonic Cruiser. It didn’t look like anything else out of Boeing, but the aft-set, compound-swept wings and the engine location made the aircraft look very much like a series of supersonic designs from the 1990s by Sukhoi, a Russian aircraft company with which Boeing has partnered to develop a regional jet airliner. Late in 2002, Boeing cancelled the Sonic Cruiser—but don’t be surprised if this resilient gene strand pops up somewhere else before too long.

The coelacanth is a creature that was so well adapted to its marine reef environment that it did not need to evolve despite more than 300 million years of existence. In St. Augustine, Florida, Northrop Grumman still builds the E-2C Hawkeye for the U.S. Navy and export customers. The long-wing, twin-engine airplane, with a radar dish sitting on its back like a friendly UFO, no fewer than four vertical tails, and its Grumman folding wing, which looks double-jointed but isn’t, is entirely suited to the task of carrying a radar off a carrier. The production line started moving in 1960 and shows no signs of stopping soon.

Lockheed Martin’s U-2 is a serial coelacanth. The Central Intelligence Agency, which sponsored the original design in 1954, planned to build 30 airplanes and fly them until Soviet surface-to-air missiles improved to the point where the aircraft could be shot down. The CIA thought this would happen about 1960, and it did, but the agency continued fielding the U-2 because of its ability to carry heavy loads to high altitudes. The production line was restarted once in 1967 and again in the early 1980s, and every few years Lockheed Martin floats a proposal to start it yet again.